I guess it could be done, if there was quick couplings for cooling liquid and current. But this is heavy, expensive and complicated compared with a more permanently fixed battery. It can be charged in just 45 min anyway, so the practicality will only be for longer flights, needing several re chargings, and then you end up in the problems Peter is talking about. Technically feasible – yes, a good solution in a real worlds scenario – probably not.
LeSving wrote:
It can be charged in just 45 min anyway
I fear this may end up going the same way as our prior discussion about electric cars, but an 80 knot aeroplane with an endurance of <1 hour that needs a 45 minute charge on each landing is not a practical proposition for A-B travel.
To give context, the PA17 goes about the same speed and carries a similar payload but is still quite limiting for A-B, even with 2.5 hours endurance and ~1 minute needed to refill the tank upon landing.
IMO electric aircraft may well start with a development of the Kers system as used in Formula 1. It produces around 6 seconds of extra boost. In formula 1 this is equivalent to 80hp with a fuel saving of around 15kg. The weight addition would be around 35 – 40kg.
But imagine you used this system for instance at the start of take off you could reduce an engine size and an engine weight and need less fuel which would also reduce weight
You would also have 6.6 seconds of regular boost as and when needed throughout a flight. This could be combined with new materials with built in solar cells. Or in some IFR aircraft that 80hp could.be very useful in de icing equipment. It might mean difference training. The technology is already there for this and it’s getting better all the time. We didn’t get from the Kitty Hawk to Concorde in less than a century by blinkered thinking.
gallois wrote:
We didn’t get from the Kitty Hawk to Concorde in less than a century by blinkered thinking.
Indeed. We got there through some fairly focused development on the fundamentals of flight: engines of ever-increasing power and wings/structures of ever-decreasing drag.
I’m not sure how KERS features. Surely you need to charge it up (i.e. do some braking) before you can utilise it, so how does that work for takeoff? If you think about it, aircraft already ‘recover’ a lot of energy through a long descent at a relatively low power setting towards the end of the flight.
KERS works with cars because they (particularly racing cars) spend a lot of time slowing down, and one has the opportunity to harvest that energy rather than just using it to turn brake pads into heat.
You could start with a charged KERS system. One of the biggest uses of power is to get the aircraft rolling and up to speed. 80hp is a long way towards another engine on a small aircraft. In formula.1 we are talking of engines around the 2000 cc here
Larger engines could produce more stored energy.
There are many ways you can recharge an engine in formula 1 it is not the braking as in pushing on a brake pedal but the engine braking.
The same is true in an aircraft’s descent. Also once in the cruise there is a certain amount of power available to recharge a KERS. Both piston and jet engines waste a great deal of energy.
So the system recharges on descent you now have extra power to use in a go round where a great deal of fuel would be required. Similarly any change of level would either give you extra power or would recharge the system.
But you seem to think that technology, whatever that may be, stays as it is now. The Kers or similar system would of course have to be developed to suit a different purpose.
They used to spin up autogyros for jump take-offs nearly a century ago. Other than that I don’t see a lot of use for a KERS-like system, particularly when if you have an electrical aircraft you can store much larger amounts of energy. Didn’t one of the electric trainers use the prop to partially recover some of the energy used in circuits?
I have often thought that a starternator could be used to improve take-off performance. You could use a small battery pack to provide e.g. 5 minutes of high power then an IC engine to sustain the aircraft in flight whilst recharging the pack. Motors will give you 7-8 horsepower per kg, so for a small aircraft you could get a huge power boost without adding a lot of weight.
Re. electric aircraft for Orkney inter-island services: look at the distances. Flight times are less than standard circuit lessons. The battery exchange need not be only at home base. Airline can have battery packs on charge, ready for exchange, using wind or tidal turbine electricity. Avgas has to be brought by a special tanker, and is more expensive than on the UK mainland.
Situations like this are where commercial operations can be economic.
Orkney to Inverness and Aberdeen would not work.
Orkney to Shetland might.
The Danish Air Force is getting two Velis Electro from Pipistrel 
https://forsvaret.dk/da/nyheder/2021/elektrisk-fly/
Here is another investor milking project / research grant consumption project
The eFlyer 800
Looking at the specs, the investor bundle will include patents on nuclear fusion, levitation, and drag reduction by electrostatic effects (believed to be how UFOs can fly so fast through the atmosphere).
